The present invention relates to a dental tool, in particular a dental tool for grinding teeth.
Dental tools for grinding teeth, as are known from for example from the generic disclosure of EP 71 611 B1, are used in dental preparatory techniques for both pre-grinding (roughing) and fine grinding (smoothing) operations. In these grinding or abrading processes the dentist and also the patient want the procedure to be completed as fast as possible. Here, however, a conflict of interests arises. The dentist must prepare the tooth in such a way that it can subsequently be restored again. The dentist should not remove too much material. Nor should there be any avoidable damage caused by, for example, high preparation temperatures. In this regard it should be noted that normally the amount of material removed should be as small as possible. A preparation is needed that is gentle on the tooth substance and that preserves it.
This, however, is not possible for all preparatory work. For instance, when a tooth is prepared that is to be provided with a crown or bridge in a later step, a relatively large amount of material must be removed by the dentist depending on the individual case. The instruments used for this are available with different grain sizes. Many dentists prefer coarse grinding instruments to achieve a reduction of the dental enamel as quickly as possible. The known grinding instruments, however, are in need of improvement as to their efficiency, i.e. a fast reduction of the dental enamel is desirable from the viewpoint of the dentist and also from that of the patient.
It is one object of the present invention to provide a dental tool that in practice achieves a higher removal rate with respect to a surface to be treated. Other objects of the invention are described herein.
According to the invention this object is achieved by a dental tool, in particular a tool for grinding teeth, comprising a grinding head and a rotatingly drivable shaft, the grinding head having on its surface at least one elevated portion that, during revolution of the grinding head, works or treats a surface to be prepared and defines a circle of rotation. The dental tool is characterized in that the elevated portion comprises and edge, the edge forms the side line of a surface that is situated at least at the leading side of the edge and that is recessed relative to the rotation circle defined by the edge.
The dental tool of the invention is characterized by several advantages. Due to the arrangement of a grinding head having at least one elevated portion comprising an edge, and in contrast to known grinding instruments that have a conical or cylindrical surface, a higher contact pressure is achieved at the working area or elevated portion at a constant pressure force exerted by a dentist during the grinding or abrading operation, which results in a greater amount of removal. In the known grinding instruments a larger contact surface contacts the tooth per unit time, so that the constant contact force is distributed over a larger surface area.
At the same time, however, the tooth surface may be worked or treated over the entire external length of the grinding head of the invention. As a result, in various embodiments described herein the trailing sections of the edge contact the tooth surface during each revolution of the grinding head at a certain time delay that depends on the rotational speed of the grinding head and the pitch or other configurational arrangement of the elevated portion.
The configuration of a grinding head having an elevated portion comprising an edge has the additional effect that edges represent a known geometrical shape and, in addition, have a great strength, which is of special importance to grinding tools. Moreover, edges can be produced in different ways, depending on the shape of the blank used in manufacturing the tool, so that a simple and inexpensive production method can be chosen.
Because the edge forms the side line of a surface that is situated at least at the leading side of the edge and is recessed relative to the rotation circle defined by the edge, in the course of rotation of the dental tool the elevated edge or side line of the recessed surface comes into contact with the tooth surface to be treated from its initial contact point up to its end or trailing contact point. In this manner, both the interests of the dentist and those of the patient to be treated are satisfied with the dental tool of the invention by way of the trailing removal of dental enamel through the higher contact pressure per working area at a constant contact force exerted by a dentist.
Preferably, the grinding head is substantially conical, so that the known advantages of conical shaped grinding heads are additionally achieved by the conical grinding heads of the invention.
According to another advantageous aspect of the invention, the recessed surface or surfaces may be planar (that is, substantially flat in cross-section) or have a concave curvature. Such shapes of the surfaces can be produced in a particularly easy manner. Moreover, instead of being concavely curved, the recessed surface may also consist of two sections intersecting each other at an obtuse angle, as in an indented wedge shape.
To improve the efficiency of the dental tool of the invention, not only one edge, but several edges of a similar type should be formed on the circumference of the grinding head. It is possible for example to form a plurality of adjacent, recessed planar surfaces on the outer circumference of the grinding head that are separated one from the next by elevated curved portions remaining in the originally conical grinding head following tooling. Alternatively, two planar surfaces may also adjoin each other directly.
When the elevated curved portion is positioned in the outer (rotation) circle of the dental tool of the invention, the configuration allows excellent guidance of the tool on the tooth to be treated without impairing the other inventive effects.
According to an alternative embodiment of the dental tool of the invention, the elevated portion comprises an edge that is threaded over the length of the grinding head. As a result, a multitude of point-like sections of the edge simultaneously engage into the surface of the tooth per time unit and at a corresponding pitch of the thread-like edge. Hence, although the contact pressure as divided among the multitude of engaging pointlike sections, at a constant contact force per working surface area, is smaller than would occur with a single engaging point-like section, it is still greater than the contact pressure of known cylindrical or conical heads. Moreover, the working surface is still at least twice the size of a smooth circumferential surface of the conventional grinding instruments and may also be many times that size provided that the pitch of the thread is appropriately chosen.
To achieve a production of a thread-like edge as simply as possible, the elevated portion may comprise a rounded elevated surface similar to a screw thread.
According to a further alternative embodiment of the dental tool of the invention, the edges are part of a honeycomb-like structure consisting of alternating fields circumferentially offset one from the next along the longitudinal length of the grinding head. Preferably, each of said alternating fields comprises a plurality of elevated portions comprising edges, and a plurality of recessed surfaces adjoining said edges. This is of advantage insofar as, in the case of a substantially circular cross-section of the grinding head of the invention, a multitude of edges can be formed on the surface of the grinding head.
According to another aspect of the invention, the grinding head comprises at least two longitudinally successive sections and the edges of the first section are arranged in a circumferentially-offset fashion relative to the edges of the other section. Such a configuration guarantees that a given edge contacts the tooth only sectionwise, resulting in a high contact pressure. This above embodiment can be implemented in a particularly simple way when the edges extend in the longitudinal direction of the dental tool, because such a configuration yields a particularly simple and easily-producible geometrical shape.
The offset arrangement of the edges can specifically be chosen such that the edges of the next sections but one are substantially identical in orientiation. Other alternations of offset among the multiple sections will be recognized by those skilled in the art in view of the present disclosure. A particularly advantageous relation between treatment time and removal rate can thereby be achieved.
According to another development of the invention, when several edges are provided that intersect one another forming a rhombic pattern, it is possible to remove a great amount of material without the above-explained drawbacks of the prior art being observed.
A configuration that can be produced in a particularly simple way is obtained when a concave curvature is provided at both sides of a rounded edge, resulting in an approximately waved design. Such a design can not only be produced easily, but due to the absence of corners is also devoid of any stress peaks, and yields a dental tool has a particularly long service life.
In addition, and in contrast to conventional conical grinding instruments, the surface area of the grinding head is macroscopically enlarged, whereby an increased number of grinding grains can be placed on the grinding head.
In all of the above-mentioned preferred embodiments of the dental tool according to the invention, the surface of the grinding head preferably has diamond grinding grains placed thereon for increasing the removal rate. The diamond grains may either have the same grain size or different grain sizes. The grain sizes of the diamond grains range from about 5 to 250 xcexcm, preferably 100 to 180 xcexcm. The selection of the grain size will, in turn, have an effect on the removal efficiency with respect to the dental enamel and should thus be adapted to the requirements of the dental tool.
Further advantages and features of the present invention will become apparent from the following detailed description of inventive embodiments of a dental tool in conjunction with the attached drawings.